Implant deployment devices for introducing intraluminally a stent, stent graft or other implant or prosthesis are typically provided with an outer sheath within which there is provided an implant support element or deployment mechanism such as an inner catheter or cannula which may include a pusher rod and dilator. The sheath has the function of containing various components of the implant deployment device, and in particular the implant, therewithin during the intraluminal introduction procedure. This flexes and twists as it passes through the various lumens of the patient, until it reaches the location at which the implant being carried needs to be positioned. The sheath is typically of a construction that is flexible so it can be passed relatively easily through lumens of a patient and yet be able to withstand rotational torque. Rotation is important during the implant placement process. For example, the implant may need to be rotated at the implantation site to ensure that it is placed in the correct orientation. For this purpose, the sheath is of a length that extends, normally, to a dilator tip at the distal end of the implant deployment device and also to outside the insertion site in the patient and, for example, to outside the femoral artery. This end is typically termed the proximal end. This proximal end of the sheath typically has fitted integral therewith a plurality of manipulation elements for controlling the introduction of the sheath into the patient, and the release of the implant, as well as for supplying various fluids during the medical procedure, such as saline solution or necessary medicaments.
Typically, the implant is located at the end of a pusher rod, which is itself flexible, and which extends from the proximal end to the distal end of the implant deployment device and within the sheath.
A problem can occur when using prior art implant deployment devices, and, in particular, when it is necessary to twist the implant deployment device in order to rotate the distal end of the implant deployment device to ensure correct orientation of that end of the device, and, in the case of deployment of a prosthesis or implant, correct orientation of the implant in the patient. With prior art devices, when the surgeon attempts to rotate the proximal end of the deployment device, once the inner catheter has been unlocked from the sheath, that is, when the surgeon rotates the end external to the patient, relative rotation between the pusher member and the sheath and therefore incorrect rotation of the distal end of the deployment device can occur. This can result in incorrect placement of an implant and in some cases can also lead to twisting of the implant because of the torque generated between the sheath and the pusher member at the distal end of the device.
U.S. Pat. No. 4,682,981 discloses a medical device for introducing a catheter into a blood vessel of a patient. A locking device has grooves and ribs provided in a main body of the medical device and in a dilator portion of the medical device. The ribs and grooves interengage and thus prevent movement between the main body and the dilator portion. The ribs and grooves thus act as a locking device, which prevents both rotational and axial movement between the main body and the dilator. With this device it would not be possible to manipulate the implant support element in the axial direction (for example, to move a pusher member distally) whilst the locking device is locked. Once unlocked, both axial and rotational movement are enabled. Therefore, this lock is seen only as an alternative to conventional sheath locking devices, which lock longitudinally and rotationally until released.
U.S. Pat. No. 6,589,251 addresses the problem of rotational movement of the sheath relative to the inner catheter or pusher rod. It discloses a multi-sheath delivery catheter in which telescopically arranged sheaths are respectively attached to a handle. The transverse shapes of the facing surfaces are complementary and non-round in cross-section. For example, they may be square, triangular, oval or D-shaped. Whilst this arrangement prevents relative rotation between the handles, the solution is unsatisfactory for several reasons. A non-round cross-section has increased likelihood of jamming of the telescopic components. Furthermore, they suffer from uneven flexibility in different radial directions, and increased risk of kinking. It is also difficult to make such devices sufficiently small for many medical applications.